1. Field of the Invention
The present invention generally relates to electronic devices having a battery unit or an AC adaptor therein which can be detached therefrom and exchanged from one to the other, and particularly relates to an electronic device to which electric power can be supplied from an external battery unit or an external AC adaptor.
2. Description of the Prior Art
As a result of miniaturization of electronic devices based on the development of the semiconductor technology, the miniaturization of electronic equipment has brought about a portable use of such equipment. Portable electronic equipment, such as portable personal computers, having an exchangeable battery unit therein is now available. Unfortunately, the life of such a battery unit is about ten hours at best. Thus, such equipment when being used other than for portable use is typically provided with electric power through an external AC adaptor 47 as shown in FIG. 1. That is, such equipment is provided with an input port 44 for receiving DC power, through which the output voltage of the AC adaptor is supplied.
However, having an external AC adaptor separate from the electronic equipment means an inconvenience of having around an object which does not seem to be absolutely necessary. It is especially so for those who use such equipment indoors in the office or in households. An expectation for more convenience in portable equipment has brought about equipment having a container therein which can store a battery unit or an AC adaptor detachable and exchangeable with each other. Furthermore, while having such a container for a battery unit and an AC adaptor, some equipment can be provided with DC power from an external AC adaptor in order to charge a battery unit stored in the container.
However, in such equipment having a container for a battery unit and an AC adaptor and capable of using an external AC adaptor, an input port of the equipment for receiving DC power cannot be used other than for charging the battery unit therein. Also, it cannot be used for charging the battery unit when the equipment itself is being used. Thus, if a user wishes to charge the battery unit while using the equipment, the user has to purchase a separate charger in order to charge the battery unit detached from the equipment.
Accordingly, in the field of electronic equipment having a battery unit or an AC adaptor detachable and exchangeable with each other, there is a need for electronic equipment which not only can use an external DC power supply for charging the battery unit inside the equipment but also can charge the battery unit detached from the equipment and can use an expansion battery unit in addition to the battery unit inside the equipment.